President Obama praised Hagel as “an American patriot who fought and bled for our country” and said he will count on his new cabinet member’s “judgment and counsel” as the United States wraps up its campaign in Afghanistan and stays "ready to meet the threats of our time."

Although the president touted the Senate confirmation, only four GOP senators voted for Hagel.

In fact, last week, 15 Republicans sent a letter to the president asking him to withdraw his nominee given the level of opposition.

“It would be unprecedented for a Secretary of Defense to take office without the broad base of bipartisan support and confidence needed to serve effectively in this critical position,” the letter read. “Over the last half-century, no Secretary of Defense has been confirmed and taken office with more than three Senators voting against him…. The occupant of this critical office should be someone whose candidacy is neither controversial nor divisive.”

GOP disapproval stems, in part, from Hagel’s past statements on such sensitive issues as Israel and Iran.

In 2007, Hagel said that the "Jewish lobby intimidated lawmakers," according to news reports. He also denounced the war in Iraq, the Patriot Act and U.S. policies on military intervention. Additionally, opponents, such as the Emergency Committee for Israel (ECI), tried to paint Hagel as being too soft on Iran, given his vote against unilateral sanctions against the country.

However, Hagel has supported multilateral sanctions against the regime, such as those imposed by the United Nations. And, while he has pushed for more diplomatic approaches, rather than military threats, toward the Middle Eastern country, he has since said that military options should remain open, according to FactCheck.org.

William Kristol, chairman of ECI, which aired ads and created a website to oppose Hagel’s confirmation, said despite their loss, they believe their campaign had a positive impact.

"We fought the good fight, and are proud to have done so,” he said in a statement.

He later added, “We take some comfort in Mr. Hagel's confirmation conversions on the issues of Israel and Iran, and do believe that, as a result of this battle, Mr. Hagel will be less free to pursue dangerous policies at the Defense Department and less inclined to advocate them within the administration.”

Beyond his previous incendiary statements, including his censure of conservative figureheads like Rush Limbaugh, Republicans said they are concerned that Hagel is not suited to meet the challenges facing the department; such as Iran’s relentless nuclear program, North Korea’s escalating threats of a nuclear attack, potentially deep budget cuts, a strategic pivot to the Asia-Pacific region, the ongoing Global War on Terror, the continued conflict in Syria, and other aftershocks of the Arab Spring.

They said his shaky performance at the confirmation hearings reinforced their fears.

“There is simply no way to sugarcoat it: Senator Hagel’s performance before the Senate Armed Services Committee was remarkably inept,” said Texas Republican John Cornyn in statements on the Senate floor Feb. 26, “and we should not be installing a Defense Secretary who is obviously not qualified for the job, and who holds dangerously misguided views on some of the most important issues facing national security policy for our country.”